The greatest advantage of a multimodal imaging is that it combines the strengths of multiple imaging platforms on the same subject. This provides with flexible tools for longitudinal tracing and measurement of delivered transgenes. To take the advantages of multimodal imaging systems, multiple reporter genes have to be expressed in cis or as a single fusion gene product. Multimodality reporters consisting of combinations of fluorescent proteins of various colors (CFP, GFP, YFP, or RFP), bioluminescence (Firefly luciferase or Rennila luciferase), and nuclear medical imaging (Truncated human herpes simplex virus type 1 thymidine kinase (HSV1tk) or sodium iodine symporters) have been previously generated and utilized in numerous applications (see Rome C, Couillaud F, Moonen C T. Gene expression and gene therapy imaging. Eur Radiol. February 2007; 17(2):305-319; Kang J H, Chung J K. Molecular-genetic imaging based on reporter gene expression. J Nucl Med. June 2008; 49 Suppl 2:164S-179S.)
Functional bi- or tri-modal reporter genes produced by fusing coding regions of fluorescent proteins, luciferase, or HSV1tk were generated and these multimodal reporters driven by a ubiquitous promoter were primarily for oncological applications (see Kesarwala A H, Prior J L, Sun J, Harpstrite S E, Sharma V, Piwnica-Worms D. Second-generation triple reporter for bioluminescence, micro-positron emission tomography, and fluorescence imaging. Mol. Imaging. October-December 2006; 5(4):465-474; Kim Y J, Dubey P, Ray P, Gambhir S S, Witte O N. Multimodality imaging of lymphocytic migration using lentiviral-based transduction of a tri-fusion reporter gene. Mol Imaging Biol. September-October 2004; 6(5):331-340; Ponomarev V, Doubrovin M, Serganova I, et al. A novel triple-modality reporter gene for whole-body fluorescent, bioluminescent, and nuclear noninvasive imaging. Eur Nucl Med Mol Imaging. May 2004; 31(5):740-751; Ray P, De A, Min J J, Tsien R Y, Gambhir S S. Imaging tri-fusion multimodality reporter gene expression in living subjects. Cancer Res. Feb. 15, 2004; 64(4):1323-1330).
Fibroblast growth factor 1 (FGF1) also known as acidic fibroblast growth factor (see Wang W P, Lehtoma K, Varban M L, Krishnan I, Chiu I M. Cloning of the gene coding for human class 1 heparin-binding growth factor and its expression in fetal tissues. Mol Cell Biol. June 1989; 9(6):2387-2395), is widely expressed in a variety of tissues in different stages of development. While no abnormality was observed in FGF1 null mice indicates highly functional redundancy in FGF family genes that consisting of at least 22 members (see Miller D L, Ortega S, Bashayan O, Basch R, Basilico C. Compensation by fibroblast growth factor 1 (FGF1) does not account for the mild phenotypic defects observed in FGF2 null mice. Mol Cell Biol. March 2000; 20(6):2260-2268). FGF1 is the universal FGF and can activate all FGFRs and results in the activation of signal transduction cascades, leading to broad biological processes, including embryonic development, cell growth, morphogenesis and remodeling (see Ornitz D M, Xu J, Colvin J S, et al. Receptor specificity of the fibroblast growth factor family. J Biol Chem. Jun. 21, 1996; 271(25):15292-15297; Zhang X, Ibrahimi O A, Olsen S K, Umemori H, Mohammadi M, Ornitz D M. Receptor specificity of the fibroblast growth factor family. The complete mammalian FGF family. J Biol Chem. Jun. 9, 2006; 281(23):15694-15700). FGF1 functions to regulate the endothelial cell migration and proliferation, and is involved in angiogenesis (see Wang W P, Lehtoma K, Varban M L, Krishnan I, Chiu I M. Cloning of the gene coding for human class 1 heparin-binding growth factor and its expression in fetal tissues. Mol Cell Biol. June 1989; 9(6):2387-2395; Chen G J, Forough R. Fibroblast growth factors, fibroblast growth factor receptors, diseases, and drugs. Recent Pat Cardiovasc Drug Discov. June 2006; 1(2):211-224).
The functions of FGF1 in neural tissues including brain and retina have been well characterized (Wang W P, Lehtoma K, Varban M L, Krishnan I, Chiu I M. Cloning of the gene coding for human class 1 heparin-binding growth factor and its expression in fetal tissues. Mol Cell Biol. June 1989; 9(6):2387-2395; Catalani E, Tomassini S, Dal Monte M, Bosco L, Casini G. Localization patterns of fibroblast growth factor 1 and its receptors FGFR1 and FGFR2 in postnatal mouse retina. Cell Tissue Res. June 2009; 336(3):423-438; Basilico C, Moscatelli D. The FGF family of growth factors and oncogenes. Adv Cancer Res. 1992; 59:115-165; Dono R. Fibroblast growth factors as regulators of central nervous system development and function. Am J Physiol Regul Integr Comp Physiol. April 2003; 284(4):R867-881). FGF-1 acts as a mitogen for neuroectoderm-derived cells by sustaining neural stem cell growth and self-renewal capacity in vitro (see Lee D C, Hsu Y C, Chung Y F, et al. Isolation of neural stem/progenitor cells by using EGF/FGF1 and FGF1B promoter-driven green fluorescence from embryonic and adult mouse brains. Mol Cell Neurosci. May 3, 2009; Nurcombe V, Ford M D, Wildschut J A, Bartlett P F. Developmental regulation of neural response to FGF1 and FGF2 by heparan sulfate proteoglycan. Science. Apr. 2, 1993; 260(5104):103-106; Bartlett P F, Brooker G J, Faux C H, et al. Regulation of neural stem cell differentiation in the forebrain. Immunol Cell Biol. October 1998; 76(5):414-418). Mitogenic effect and modulation of differentiation by FGF1 was also observed in tissues of mesoderm lineage (Jacob A L, Smith C, Partanen J, Ornitz D M. Fibroblast growth factor receptor 1 signaling in the osteo-chondrogenic cell lineage regulates sequential steps of osteoblast maturation. Dev Biol. Aug. 15, 2006; 296(2):315-328; Fu Y M, Spirito P, Yu Z X, et al. Acidic fibroblast growth factor in the developing rat embryo. J. Cell Biol. September 1991; 114(6):1261-1273; Grunz H, McKeehan W L, Knochel W, Born J, Tiedemann H. Induction of mesodermal tissues by acidic and basic heparin binding growth factors. Cell Differ. February 1988; 22(3):183-189).
The human FGF1 gene contains three protein-coding exons and a long 3-untranslated region that the whole gene spans over 120-kb. Four upstream untranslated exons, designated as 1A, 1B, 1C, and 1D, which are resulted from distinct transcriptional start sites (TSSs) in FGF1 promoter have been identified and these alternative promoters direct the tissue-specific expression of FGF1 (Payson R A, Canatan H, Chotani M A, et al. Cloning of two novel forms of human acidic fibroblast growth factor (aFGF) mRNA. Nucleic Acids Res. Feb. 11, 1993; 21(3):489-495; Myers R L, Payson R A, Chotani M A, Deaven L L, Chiu I M. Gene structure and differential expression of acidic fibroblast growth factor mRNA: identification and distribution of four different transcripts. Oncogene. February 1993; 8(2):341-349; Myers R L, Chedid M, Tronick S R, Chiu I M. Different fibroblast growth factor 1 (FGF1) transcripts in neural tissues, glioblastomas and kidney carcinoma cell lines. Oncogene. Aug. 17, 1995; 11(4):785-789).
FGF1B (F1B) is the major transcript within the human brain and retina (Myers R L, Ray S K, Eldridge R, Chotani M A, Chiu I M. Functional characterization of the brain-specific FGF1 promoter, FGF-1.B. J Biol Chem. Apr. 7, 1995; 270(14):8257-8266) while -1A transcript predominates in kidney (Myers R L, Payson R A, Chotani M A, Deaven L L, Chiu I M. Gene structure and differential expression of acidic fibroblast growth factor mRNA: identification and distribution of four different transcripts. Oncogene. February 1993; 8(2):341-349), and -1C and -1D transcripts predominate in vascular smooth muscle cells and fibroblasts (Chotani M A, Payson R L, Winkles J A, Chiu I M. Human fibroblast growth factor 1 gene expression in vascular smooth muscle cells is modulated via an alternate promoter in response to serum and phorbol ester. Nucleic Acids Res. Feb. 11, 1995; 23(3):434-441). The expression of F1B mRNA is restricted to the sensory and motor nuclei in the brain stem, spinal cord, and other areas that are known to be abundant for NSPCs (Alam K Y, Frostholm A, Hackshaw K V, Evans J E, Rotter A, Chiu I M. Characterization of the 1B promoter of fibroblast growth factor 1 and its expression in the adult and developing mouse brain. J Biol Chem. Nov. 22, 1996; 271(47):30263-30271).
Transgenic mouse in which an SV40 T antigen (Tag) was placed under the control of F1B promoter resulted high incidence of tumors in olfactory bulb, ventral forebrain, subventricular zone, thalamus, striatum, and tegmental area (Chiu I M, Touhalisky K, Liu Y, Yates A, Frostholm A. Tumorigenesis in transgenic mice in which the SV40 T antigen is driven by the brain-specific FGF1 promoter. Oncogene. Dec. 14, 2000; 19(54):6229-6239; Weiss W A, Israel M, Cobbs C, et al. Neuropathology of genetically engineered mice: consensus report and recommendations from an international forum. Oncogene. Oct. 24, 2002; 21(49):7453-7463). Transgenic GFP expression using F1B promoter driven vector facilitate isolation of GFP positive neural stem/progenitor cells from the developing and adult mouse brain tissue (Lee D C, Hsu Y C, Chung Y F, et al. Isolation of neural stem/progenitor cells by using EGF/FGF1 and FGF1B promoter-driven green fluorescence from embryonic and adult mouse brains. Mol Cell Neurosci. May 3, 2009; Hsu Y C, Lee D C, Chen S L, et al. Brain-specific 1B promoter of FGF1 gene facilitates the isolation of neural stem/progenitor cells with self-renewal and multipotent capacities. Dev Dyn. February 2009; 238(2):302-314). Limited by the depth resolution and penetrating ability associated with green fluorescence protein, F1B-GFP mouse was not able to demonstrate the whole body distribution of GFP to reflect the F1B promoter activity in vivo.
However, the transgenic mouse model with tissue-specific trimodality reporter expression has not been described yet.